Adventitious shoot regeneration from the leaves of some pear varieties (Pyrus spp.) grown in vitro

The pear (Pyrus spp.) is one of the most important temperate fruit crops. A complete protocol for adventitious shoot regeneration was developed from the leaves of four pear varieties grown in vitro: Abbe Fetel, Yali, Packham’s Triumph and Aikansui, and the Chinese rootstock variety Duli. Shoot explants were collected from the field and cultured in vitro in Murashige and Skoog (MS) media supplemented with 1.0 mg·L⁻¹ 6-benzylaminopurine (BA) and 0.1 mg·L⁻¹ indole-3-butyric acid (IBA). After four weeks, leaf explants of all 5 varieties grown in vitro were excised and cultured in MS media supplemented with 0.0 mg·L⁻¹, 0.2mg·L⁻¹, 0.5 mg·L⁻¹, 1.0 mg·L⁻¹ and 2.0 mg·L⁻¹ naphthaleneacetic acid (NAA) and 5.0 mg·L⁻¹ BA or with 1.0 mg·L⁻¹, 2.0 mg·L⁻¹ and 4.0 mg·L⁻¹ thidiazuron (TDZ). The cultures were maintained in darkness for 21 days for shoot induction in the shoot induction medium (IM), then transferred to the shoot expression medium (EM) in 1.0 mg·L⁻¹ TDZ without any auxins and kept in a growth room at (25±2)°C under a 16/8 h light/dark photoperiod regime for 8 weeks. Finally, the shoots were transferred to the MS shoot elongation medium (SEM) supplemented with 0.2 mg·L⁻¹ BA, 0.1 mg·L⁻¹ IBA and 0.2 mg·L⁻¹ gibberellic acid (GA₃). A combination of TDZ and NAA had a significant effect on the number of shoot regenerations in all 5 tested varieties. The maximum mean number of shoots and maximum number of shoots per leaf obtained from Yali variety were 11.8 (P⩽0.001) and 22, followed by Aikansui with 6.6 (P⩽0.001) and 4.6, and Duli with 8 (P⩽0.001) and 12, all arising from the combination of 0.2 mg·L⁻¹ NAA with 1.0 mg·L⁻¹ TDZ. For Packham’s Triumph and Abbe Fetel, the maximum mean number of shoots and maximum number of shoots per leaf were 5.6 (P⩽0.001), 4.8 and 8 (P⩽0.001), and 11, respectively, from the combination of NAA (1.0 mg·L⁻¹) and TDZ (2.0 mg·L⁻¹). Abbe Fetel was the only variety which produced significantly higher adventitious shoots from the two different combinations of 1.0 mg·L⁻¹ NAA and 5.0 mg·L⁻¹ BA (P⩽0.05), and 2.0 mg·L⁻¹ NAA and 5.0 mg·L⁻¹ BA (P⩽0.01). Some of the most prominent problems associated with shoot proliferation and regeneration were also observed and discussed in this paper.     

Estimating the potential of rainfed agriculture in India: Prospects for water productivity improvements

A detailed district and agro-ecoregional level study comprising the 604 districts of India was undertaken to (i) identify dominant rainfed districts for major rainfed crops, (ii) make a crop-specific assessment of the surplus runoff water available for water harvesting and the irrigable area, (iii) estimate the efficiency of regional rain water use and incremental production due to supplementary irrigation for different crops, and (iv) conduct a preliminary economic analysis of water harvesting/supplemental irrigation to realize the potential of rainfed agriculture. A climatic water balance analysis of 225 dominant rainfed districts provided information on the possible surplus runoff during the year and the cropping season. On a potential (excluding very arid and wet areas) rainfed cropped area of 28.5 million ha, a surplus rainfall of 114 billion m³ (Bm³) was available for harvesting. A part of this amount of water is adequate to provide one turn of supplementary irrigation of 100 mm depth to 20.65 Mha during drought years and 25.08 Mha during normal years. Water used in supplemental irrigation had the highest marginal productivity and increase in rainfed production above 12% was achievable even under traditional practices. Under improved management, an average increase of 50% in total production can be achieved with a single supplemental irrigation. Water harvesting and supplemental irrigation are economically viable at the national level. Net benefits improved by about threefold for rice, fourfold for pulses and sixfold for oilseeds. Droughts have very mild impacts on productivity when farmers are equipped with supplemental irrigation.     

Biological nitrogen fixation by two Acacia species and associated root-nodule bacteria in a suburban Australian forest subjected to prescribed burning

Purpose

Prescribed burning is a forest management practice which can lead to nitrogen (N)-limited conditions. This study aimed to explore whether biological N₂ fixation (BNF) remained the main source of N acquisition for two understorey Acacia species in a Eucalyptus-dominated suburban forest of subtropical Australia, 3 to 6 years after prescribed burning. Root-nodule bacteria associated with these acacias were also characterised to unravel the differences in rhizobial communities between sites and species.

Material and methods

Two sites, burned 3 and 6 years before sample collection, were selected within a dry subtropical forest of south-east Queensland, Australia. Leaves were collected from individuals of Acacia disparrima and A. leiocalyx at each site to determine leaf total carbon (C) and N content, C and N isotope composition (δ¹³C and δ¹⁵N) and the percentage of N derived from atmospheric N₂. Nodules were harvested from both acacia species at each site to isolate root nodule bacteria. Bacterial isolates were processed for 16S rDNA gene sequencing.

Results and discussion

Generally, no differences were found in plant physiological variables between the two acacia species. Six years after the fire, both species still depended upon BNF for their N supply, with a higher dependence in winter than in summer. Fire, although of low intensity, was likely to have created a N-limited environment which induced the reliance of legumes on BNF. Root nodule bacteria were dominated by non-rhizobial endophytes, mainly from the Firmicutes phylum. No difference in nodule bacterial diversity was found between sites. The relative abundance of rhizobial genera varied amongst plant species and sites, with a shift in dominance from Bradyrhizobium to Rhizobium species between sites 1 and 2.

Conclusions

Our results show that even 6 years after burning, ecosystem remained under N stress and BNF was still the main mechanism for N acquisition by the understorey legumes.

     

Effect of cement dust treatment on some phylloplane fungi of wheat

The percent frequency and number of colonies cm^?2 leaf area of all the test fungi decreased significantly at the higher doses of cement dust during both pre- and post inoculation treatments. However, the population of some fungi increased at the low dose only. Stimulatory as well as inhibitory effect of cement dust on colony growth of the test fungi were observed at different concentrations of cement dust (500, 1000, 1500, and 2000 μm mL^?1).     

Resistance to ETEC F4/F18–mediated piglet diarrhoea: opening the gene black box

Diarrhoea, a significant problem in pig rearing industry affecting pre- and post-weaning piglets is caused by enterotoxigenic Escherichia coli (ETEC). The ETEC are classified as per the fimbriae types which are responsible for bacterial attachment with enterocytes and release of toxins causing diarrhoea. However, genetic difference exists for susceptibility to ETEC infection in piglets. The different phenotypes found in pigs determine their (pigs’) susceptibility or resistance towards fimbrial subtypes/variants (F4ab, F4ac, F4ad and F18). Specific receptors are present on intestinal epithelium for attachment of these fimbriae, which do not express to same level in all animals. This differential expression is genetically determined and thus their genetic causes (may be putative candidate gene or mutations) render some animals resistant or susceptible to one or more fimbrial subtypes. Genetic linkage studies have revealed the mapping location of the receptor loci for the two most frequent variants F4ab and F4ac to SSC13q41 (i.e. q arm of 13th chromosome of Sus scrofa). Some SNPs have been identified in mucin gene family, transferring receptor gene, fucosyltransferase 1 gene and swine leucocyte antigen locus that are proposed to be linked mutations for resistance/susceptibility towards ETEC diarrhoea. However, owing to the variety of fimbrial types and subtypes, it would be difficult to identify a single causative mutation and the candidate loci may involve more number of genes/regions. In this review, we focus on the genetic mutations in genes involved in imparting resistance/susceptibility to F4 or F18 ETEC diarrhoea and possibilities to use them as marker for selection against susceptible animals.

     

Spatial variability of some nutrient constituents of an Alfisol from loess I. Classical statistical analysis

Classical statistical techniques were used to evaluate the lateral and vertical variability of some nutrient constituents, viz. NO₃, extractable K and Mg, and organic C, of a loess soil field. In all 50 sites at a 30m × 30m grid were selected within a 10 ha field situated about 25 km west of Hannover. Samples were taken at 0–30, 30–60 and 60–90 cm depths. Analysis based on cumulative probability density function showed that all properties except K in the 30–60 and 60–90 cm depths were normally distributed. K in these depths was lognormally distributed. Mean values of NO₃ increased with depth, that of K decreased and that of Mg remained nearly constant. Comparison of coeffizients of variation (CV – % variation) indicated that organic C was least variable laterally (CV = 8.7) and K the most (CV = 43.8 for 30–60 cm depth). The CV of NO₃ and Mg increased slightly with depth indicating less drastic vertical variation. The number of observations required to yield an estimate of the mean value within a prescribed accuracy and precision is shown to depend upon the nature and extent of the spatial variability of a parameter. Thus, estimated number of samples was smaller for lower CV values and vice versa. The optimum number of samples for a given property is determined by the depth in which the largest estimated number of samples is required to be taken.     

Sustainable urbanization in Southeast Asia and beyond: Challenges of population growth,land use change,and environmental health

As economic growth centres, the Southeast Asian cities feature high population pressure, unsustainable land use, environmental degradation, and large ecological footprints. It is difficult to manage environmental health and basic services for urban dwellers, and ensure optimum flow of ecosystem services in the context of rapid, unplanned, and haphazard urbanization. These challenges are particularly multifaceted in the developing countries of Southeast Asian region. This study, based on secondary sources, adopted multidisciplinary lenses, such as geographical information systems, socio‐economic perspective, and sustainability science to examine the population situation, land use change pattern, and drivers of environmental degradation in the Southeast Asian cities as well as the Dhaka megacity, and brought forth a fresh perspective to look into contemporary urban ecosystems, population dynamics, environmental health, and sustainability. It also focused on identifying the commonalities among the cities under study to create a common understanding towards promoting collaborative urban development. This study shows that the urbanization process in the Southeast Asia region is taking place mostly in an unplanned and haphazard manner. With little concern for nature, life‐supporting ecological systems, and the environment, urban spatial growth continues unabated. The data surveyed and discussed in this paper shows that the current style of urbanization in Southeast Asia can best be called unsustainable. The findings also suggest that the general wellbeing and welfare of the current and future generations in Southeast Asian cities as well as in Dhaka is at risk. The paper recommends concerted efforts towards making the urbanization process sustainable, including better urban planning, policymaking, and international and regional cooperation.     

Studies on pesticides based on coumarin. I. Antifungal activity of 6-alkyl-3-n-butyl-7-hydroxy-4-methylcoumarins

Seven 6-alkyl-3-n-butyl-7-hydroxy-4-methylcoumarins and three other related substituted coumarins were synthesised, characterised and tested for their toxicity towards mycelial growth of seven phytopathogenic fungi in culture. Rhizoctonia solani, Alternaria alternate, and Drechslera oryzae exhibited maximum sensitivity to these compounds whereas Pythium aphanidermatum, Colletotrichum falcatum, Fusarium solani and Macro-phomina phaseolina were less sensitive. The 6-n-butyl and 6-n-pentyl derivatives possessed strongest toxicity towards all fungi except C. falcatum but the corresponding 6-n-propyl derivative was inhibitory to only D. oryzae and A. alternata.     

Transgene Stacking and Coordinated Expression of Plant Defensins Confer Fungal Resistance in Rice

Transgenic rice with cleavable chimeric polyprotein and single-protein gene constructs placed under the control of single maize ubiquitin promoter were generated by Agrobacterium tumefaciens-mediated transformation. The polyprotein precursor consists of a leader peptide and two different antimicrobial proteins (AMPs), Dm-AMP1 and Rs-AFP2, from the seeds of Dahlia merckii and Raphanus sativus, respectively. These genes were linked by a 16 amino acid Ib-AMP linker peptide region isolated from the seeds of Impatiens balsamina. Average expression of Dm-AMP1 and Rs-AFP2 was 8.35?±?0.56 and 8.1?±?0.6 2 g/mg of total soluble proteins in the leaf extracts of transgenic plants. Plants transformed with polyprotein construct showed significantly improved disease resistance against Magnaporthe oryzae and Rhizoctonia solani by 90% and 79%, respectively, as compared to untransformed plants. The plants transformed with polyprotein construct were more resistant to M. oryzae compared to plants transformed with control single-gene constructs of Dm-AMP1 and Rs-AFP2. The chimeric polyprotein was cleaved and present in equimolar concentration in transgenic rice and the individual AMPs were secreted into the extracellular space. The results of in vitro, in planta, and microscopic analyses suggest that chimeric polyprotein expression has the potential to provide broad-spectrum disease resistance in rice.